I had this bug, running pae kernel in a VirtualBox VM: Disk check was running and freezed at this moment...

syslog output around crash:

****

Apr  8 16:15:53 yann-laptop NetworkManager: <info>  Activation (eth0) Stage 5 of 5 (IP Configure Commit) scheduled...
Apr  8 16:15:53 yann-laptop NetworkManager: <info>  Activation (eth0) Stage 4 of 5 (IP4 Configure Get) complete.
Apr  8 16:15:53 yann-laptop NetworkManager: <info>  Activation (eth0) Stage 5 of 5 (IP Configure Commit) started...
Apr  8 16:15:53 yann-laptop avahi-daemon[547]: Joining mDNS multicast group on interface eth0.IPv4 with address 10.0.2.15.
Apr  8 16:15:53 yann-laptop avahi-daemon[547]: New relevant interface eth0.IPv4 for mDNS.
Apr  8 16:15:53 yann-laptop avahi-daemon[547]: Registering new address record for 10.0.2.15 on eth0.IPv4.
Apr  8 16:15:53 yann-laptop dhclient: bound to 10.0.2.15 -- renewal in 33102 seconds.
Apr  8 16:15:53 yann-laptop kernel: [   44.457002] vboxguest: exports duplicate symbol RTMemExecFree (owned by vboxdrv)
Apr  8 16:15:54 yann-laptop NetworkManager: <info>  (eth0): device state change: 7 -> 8 (reason 0)
Apr  8 16:15:54 yann-laptop NetworkManager: <info>  Policy set 'Auto eth0' (eth0) as default for routing and DNS.
Apr  8 16:15:54 yann-laptop NetworkManager: <info>  Activation (eth0) successful, device activated.
Apr  8 16:15:54 yann-laptop NetworkManager: <info>  Activation (eth0) Stage 5 of 5 (IP Configure Commit) complete.
Apr  8 14:15:57 yann-laptop ntpdate[901]: step time server 91.189.94.4 offset -7198.369434 sec
Apr  8 14:16:01 yann-laptop kernel: [   51.051506] eth0: no IPv6 routers present
Apr  8 14:17:01 yann-laptop CRON[952]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
Apr  8 17:44:21 yann-laptop kernel: imklog 4.2.0, log source = /proc/kmsg started.
Apr  8 17:44:21 yann-laptop rsyslogd: [origin software="rsyslogd" swVersion="4.2.0" x-pid="514" x-info="http://www.rsyslog.com"] (re)start
Apr  8 17:44:21 yann-laptop rsyslogd: rsyslogd's groupid changed to 103
Apr  8 17:44:21 yann-laptop rsyslogd: rsyslogd's userid changed to 101
Apr  8 17:44:21 yann-laptop rsyslogd-2039: Could no open output file '/dev/xconsole' [try http://www.rsyslog.com/e/2039 ]
Apr  8 17:44:21 yann-laptop kernel: [    0.000000] Initializing cgroup subsys cpuset
Apr  8 17:44:21 yann-laptop kernel: [    0.000000] Initializing cgroup subsys cpu
Apr  8 17:44:21 yann-laptop kernel: [    0.000000] Linux version 2.6.32-19-generic-pae (buildd@palmer) (gcc version 4.4.3 (Ubuntu 4.4.3-4ubuntu5) ) #28-Ubu
ntu SMP Wed Mar 31 18:57:46 UTC 2010 (Ubuntu 2.6.32-19.28-generic-pae 2.6.32.10+drm33.1)
(...)
Apr  8 17:44:23 yann-laptop cron[710]: (CRON) STARTUP (fork ok)
Apr  8 17:44:23 yann-laptop anacron[706]: Will run job `cron.daily' in 5 min.
Apr  8 17:44:23 yann-laptop anacron[706]: Jobs will be executed sequentially
Apr  8 17:44:24 yann-laptop acpid: 39 rules loaded
Apr  8 17:44:24 yann-laptop acpid: waiting for events: event logging is off
Apr  8 17:44:24 yann-laptop cron[710]: (CRON) INFO (Running @reboot jobs)
Apr  8 17:44:25 yann-laptop kernel: [   30.573175] vboxdrv: Trying to deactivate the NMI watchdog permanently...
Apr  8 17:44:25 yann-laptop kernel: [   30.573206] vboxdrv: Successfully done.
Apr  8 17:44:25 yann-laptop kernel: [   30.573209] vboxdrv: Found 2 processor cores.
Apr  8 17:44:25 yann-laptop kernel: [   30.573558] vboxdrv: fAsync=1 offMin=0x63e518 offMax=0x63e518
Apr  8 17:44:25 yann-laptop kernel: [   30.573686] vboxdrv: TSC mode is 'asynchronous', kernel timer mode is 'normal'.
Apr  8 17:44:25 yann-laptop kernel: [   30.573689] vboxdrv: Successfully loaded version 3.1.4_OSE (interface 0x00100001).
Apr  8 17:44:25 yann-laptop kernel: [   30.651166] vboxguest: exports duplicate symbol RTMemExecFree (owned by vboxdrv)
Apr  8 15:44:28 yann-laptop ntpdate[792]: step time server 91.189.94.4 offset -7197.713072 sec
Apr  8 15:44:28 yann-laptop acpid: client connected from 812[0:0]
Apr  8 15:44:28 yann-laptop acpid: 1 client rule loaded
Apr  8 15:44:28 yann-laptop kernel: [   31.715398] vboxguest: exports duplicate symbol RTMemExecFree (owned by vboxdrv)
Apr  8 15:44:31 yann-laptop kernel: [   34.778781] Linux agpgart interface v0.103
Apr  8 15:44:32 yann-laptop kernel: [   34.824938] [drm] Initialized drm 1.1.0 20060810
Apr  8 15:44:32 yann-laptop kernel: [   34.827167]   alloc irq_desc for 18 on node -1
Apr  8 15:44:32 yann-laptop kernel: [   34.827171]   alloc kstat_irqs on node -1
Apr  8 15:44:32 yann-laptop kernel: [   34.827224] pci 0000:00:02.0: PCI INT A -> GSI 18 (level, low) -> IRQ 18
Apr  8 15:44:32 yann-laptop kernel: [   34.827266] pci 0000:00:02.0: setting latency timer to 64
Apr  8 15:44:32 yann-laptop kernel: [   34.827638] [drm] Initialized vboxvideo 1.0.0 20090303 for 0000:00:02.0 on minor 0
Apr  8 15:44:34 yann-laptop gdm-session-worker[990]: WARNING: Unable to load file '/etc/gdm/custom.conf': Aucun fichier ou dossier de ce type
Apr  8 15:44:34 yann-laptop rtkit-daemon[998]: Sucessfully called chroot.
Apr  8 15:44:34 yann-laptop rtkit-daemon[998]: Sucessfully dropped privileges.
Apr  8 15:44:34 yann-laptop rtkit-daemon[998]: Sucessfully limited resources.
Apr  8 15:44:34 yann-laptop rtkit-daemon[998]: Running.
Apr  8 15:44:34 yann-laptop rtkit-daemon[998]: Watchdog thread running.
Apr  8 15:44:34 yann-laptop rtkit-daemon[998]: Canary thread running.
Apr  8 15:44:34 yann-laptop kernel: [   37.685118] eth0: no IPv6 routers present
Apr  8 15:44:35 yann-laptop polkitd[1002]: started daemon version 0.96 using authority implementation `local' version `0.96'
Apr  8 15:44:35 yann-laptop rtkit-daemon[998]: Sucessfully made thread 995 of process 995 (n/a) owned by '114' high priority at nice level -11.
Apr  8 15:44:35 yann-laptop rtkit-daemon[998]: Supervising 1 threads of 1 processes of 1 users.
Apr  8 15:44:35 yann-laptop pulseaudio[995]: alsa-util.c: Disabling timer-based scheduling because running inside a VM.

****

It seems at least there is a big mess with ntp: we go from 16h15 to 14h15... and reboot at 17h44, but real local time was 15h44, corrected only at reboot (this one was allright).